Patent Application
20120255989
The subject matter disclosed herein relates to the art of metal joining and, more particularly, to a method of establishing filler metal chemistry for a filler rod for joining components.
High strength and oxidation resistant alloys such as nickel-based super alloys are widely used in the construction of turbomachines. The super alloys possess strength, weight, durability, and temperature properties desirable for use in turbomachine components. However, in general, super alloys have poor fusion weldability due to a tendency for liquation cracking and strain age cracking (SAC). SAC is closely related to gamma prime volume fraction, which is a function of Aluminum (Al) and titanium (Ti) content. An increase in the gamma prime fraction and, in particular Al content, increases the tendency for SAC. SAC generally occurs in a weld metal adjacent to a fusion boundary (WMATFB) region and/or propagates into a heat-affected zone (HAZ) of a welded joint. Material in the WMATFB region includes base metal resulting from dilution and filler metal added during welding. As such, the WMATFB region should include a chemistry that falls within a weldable material region to avoid, or at least lower, a tendency towards SAC.
If the WMATFB region chemistry falls within the weldable material region, cracking tendency is low. In a tungsten inert gas (TIG) welding process for example, a typical dilution ratio is about 30:70 which means 30% of the WMATFB region includes base metal and 70% of the WMATFB region includes filler metal. Accordingly, filler metal for welding a particular alloy must possess certain chemical composition and mechanical properties at elevated temperature. Presently, filler metal is selected based on chemical composition, mechanical properties, and weldability. However, in addition to possessing desirable chemical properties, filler metal must also possess certain mechanical properties and oxidation performance at elevated temperatures. Selecting a particular filler metal requires a trade off between materials having desirable chemical or mechanical properties for a particular application. Accordingly, many engineers have turned to having specific filler metals specially fabricated for a particular super alloy.
Determining a desired, non-standard, filler metal chemistry is a time consuming and costly process. Once an initial chemistry is chosen, an order is placed with a fabrication facility for the non-standard filler metal. Non-standard filler metal cannot be ordered in small quantities. An order for a filler metal having a specific chemistry generally requires a commitment of 100 lbs (45.35 kg) or more. Once received, the filler metal is used to form a joint in a welding operation and the joint is tested. If the filler metal does not have the desired properties, filler metal chemistry is adjusted, and a new order for filler metal is placed. This process continues until the desired properties are achieved. While this trial and error process ultimately leads to a desired filler metal chemistry, the cost associated with multiple orders of filler metal is prohibitive as are the costs associated with testing and warehousing spools of filler metal
According to one aspect of an exemplary embodiment, a method of establishing filler metal composition for joining components includes determining an initial desired filler metal chemistry, adjoining a first filler rod having a first portion of the desired filler metal chemistry with a second filler rod having a second portion of the desired filler metal chemistry to form a test filler rod, joining a first component formed from a first material to a second component formed from a second material at a weld joint with the test filler rod providing a filler metal portion of the weld joint, and testing the weld joint for desired mechanical, chemical and weldability properties to establish a desired filler metal composition.
According to another aspect of the exemplary embodiment, a process for establishing a desired filler metal composition for joining components includes selecting a first filler rod having a first filler metal chemistry, selecting a second filler rod having a second filler metal chemistry, twisting together the first and second filler rods forming a test filler rod having a twisted region comprising the first and second filler metal chemistries, joining a first component formed from a first material to a second component formed from a second material with a welding process employing the test filler rod, and testing a weld joint formed between the first and second components.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Joining components formed from various materials, using a welding process requires the use of filler metals having certain chemical properties. Chemical properties are specifically selected to mitigate liquation cracking and strain age cracking (SAC). SAC is closely related to gamma prime volume fraction, which is a function of Aluminum (Al) and titanium (Ti) content. An increase in the gamma prime fraction and, in particular Al content, leads to an increased tendency for SAC. SAC generally occurs in a weld metal adjacent to a fusion boundary (WMATFB) region and/or propagates into a heat-affected zone (HAZ) of a welded joint. Material in the WMATFB region includes base metal resulting from dilution of the super alloys caused by heat from the welding process, and filler metal added during the welding process. Conventionally, establishing the desired chemical properties requires a costly trial and error process. The following exemplary embodiments describe a process for establishing a desired filler metal chemistry without requiring substantial capital costs associated with purchasing, testing, and warehousing numerous lots of bulk non-standard filler rod material.
With reference to
For example, data in an SAC chart indicates that the WMATFB region of a TIG weld repair of an R108 casting base metal with Nimonic 263 filler metal is located almost exactly upon a threshold line between a weldable material range and a non-weldable material range. The threshold line has a slope that is defined in terms a ratio of Al and Ti content. Filler metal chemistry having an aluminum content that falls below the threshold line is said to have good weldability and cracking is less likely to occur. If the filler metal chemistry has an aluminum content that falls above the threshold line, weldability is said to be bad and cracking is more likely to occur. Being located on the threshold line indicates that cracking is prone to occur at the WMATFB region and HAZ under a high strain level. Thus, a filler metal chemistry that moves the WMATFB region to below the threshold line is desirable. R108 is known to possess good mechanical properties and oxidation performance properties at elevated temperatures. Hence, filler metal chemistry is selected to closely match such properties under available weldability. However, standard commercial off the shelf (COTS) filler rods having filler metal chemistry that both match the mechanical and oxidation performance properties of R108 and also maintain the WMATFB region in the weldable material range do not exist.
Accordingly test filler rod 14 includes a first filler rod 16 having a first portion of the desired non-standard filler rod chemistry and a second filler rod 18 having a second portion of the desired non-standard filler rod chemistry. First and second filler rods 16 and 18 are adjoined and twisted together to form a twisted region 20 that comprises the desired non-standard filler metal chemistry. In accordance with the exemplary embodiment shown in
Once formed, test filler rod 14 is employed in a welding process to join a first component 40 formed from a first super alloy to a second component 42 formed from a second super alloy as indicated in block 24 and shown in
If, however, the non-standard filler metal chemistry resulting from the joining of first and second filler rods does not produce the desired mechanical, oxidation, and weldability performance properties in block 28, alternative filler rods are selected as indicated in block 32 and joined to form a new test filler rod as indicated in block 34. The new filler rod is used to join the first and second components in block 24, and the resulting weld joint is tested in block 26. This process will continue until a non-standard filler metal chemistry that produces the desired mechanical, oxidation, and weldability performance properties.
At this point, it should be understood that the number and type of filler rods combined to form a test filler rod can vary. For example as shown in
It should also be understood that filler rod size or diameter can vary. For example,
At this point it should be understood that the exemplary embodiments are directed to establish desired filler rod chemistry for joining components without the need for cost, in both time and money, of purchasing and testing filler rods having non-standard filler metal chemistries. It should also be understood, that while described in terms of joining first and second distinct super alloys, that the exemplary embodiments can be employed to develop filler metal chemistries used in joining components formed from a wide array of materials, including joining components formed from substantially similar materials.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
